This is a quick button for smart phone which used audio socket.
Step 1: Video Instructions
Here is a simple method to make a quick or short cut hardware button for mart mobile phones. It uses the mic pin as input pin. Its generally pulled up by a high resistor and used to bias the mic. Here in place of mic we have used a 10K Resistor and a switch. If you press then input will vary from high - low - high . The App reads the mic port and if sees this kind of patter then consider it as a single click and does the necessary action.
In google play store search for “ iKEY” , you will find multiple free app like iKey, KeyCut, Klick, Clicky , headset droid, headset button controller etc. This app can be used to program the short or long press, single or multiple click. It can also be used a FM antenna if not used as mykey. Using mic as input pin many companies has designed swipe card reader too.